Ni-Cr type alloy materials have generally been widely used as heating elements at elevated temperatures and as electrical resistors at elevated temperatures. The reason for this favorable acceptance is that the Ni-Cr type alloy materials, as compared with the Fe-Cr-Al type alloy materials, for example, have advantages such as not being easily embrittled even after exposure to heat, exhibiting high strength and other mechanical properties at elevated temperatures, and having sufficient stability to withstand virtually all corrosive gases except sulfide gases. On the other hand, they have disadvantages such as lower degrees of electrical resistance, larger electrical resistance temperature coefficients at varying temperatures from room temperature through elevated temperatures, and slightly lower maximum working temperatures than the Fe-Cr-Al type alloys. Moreover, they do not fully satisfy other requirements such as having an ability to resist the action of acids.
Generally, it is possible to improve the ability of Ni-Cr type alloy materials to resist acid and enhance their electrical resistance up to the level of 115 .mu..OMEGA.-cm by fixing their Cr contents in the range of 40 to 45 atom%. However, this increase in the Cr contents results in degradation of workability of alloy materials. Normally, therefore, Ni-Cr type alloy materials having Cr contents controlled to the neighborhood of 20 atom% for the purpose of ensuring ample cold-moldability are used. Efforts to improve the aforementioned disadvantages by the incorporation of Al and Si have been separately continued. Since it has been ascertained that their incorporation heavily impairs workability even to the extent of rendering cold working or coiling impracticable the incorporation of Al and Si is now limited to 3 atom% at most.